LUMINESCENT DETERMINATION OF TOTAL BITTER SUBSTANCES CONTENT IN HOPS

Abstract

The possibility of determination of total bitter substances content in hops by sensitized Tb(III) ions luminescence is studied. The ligands under study contain a dicarbonyl fragment and, obviously, similar to β-diketones form complexes with ions of lanthanides. The spectroscopic characteristics of hop bitter substances are studied. The study shows that aqueous-ethanol solutions of these ligands have an intensive absorption band in UV region of spectrum, energy of their triplet level is close to energy of the excited level of Tb(III) ion that makes transmission of excitation energy to the Tb(III) ion possible. It is established, that in the presence of hop bitter substances lifetime of the excited state of an ion of Tb (III) considerably increases in comparison with lifetime of terbium aqua ion that can confirm formation of complexes. The dependence of luminescence intensity of complexes on concentration of terbium, acidity, type of solvent is investigated. Optimal luminescence intensity of Tb(III) ion is found in neutral mediums at pH 5.8-6.1 and considerably increases in the presence of alcohols – ethanol and isopropanol. The surface-active substances (cetyltrimethylammonium chloride, cetylpyridinium chloride, sodium dodecyl sulfate, triton X-100, tween-80), and donor-active agents (1,10-phenanthroline, 2,2 ‘-dipyridyl, triphenylphosphine oxide, trioctylphosphine oxide , β-cyclodextrin) don’t influence intensity of the luminescence of complexes or reduce it. The detection limit of bitter substances in extracts of hop makes 0,01 mkg/ml.

Keywords

• гіркі речовини хмелю, сенсибілізована люмінесценція іона Tb (III)